Light sensitive control system for automobile lighting circuits



L. COLLINS 3,349,281

LIGHT SENSITIVE CONTROL SYSTEM FOR AUTOMOBILE LIGHTING CIRCUITS Oct. 24, 1967 Filed Dec. 29, 1964 I MANUAL OR AUTOMATIC IGNITION HEAD LAMPS TAIL LAMPS BATTERY [N VENTOR. Zer /7 5 30/4 ATTORNEY United States Patent ABSTRACT OF THE DISCLOSURE A circuit for energizing the head and tail lamps of an automobile including a light sensor which causes energization of a relay coil when ambient light decreases. Relay coil moves an armature otf a first contact to permit a transistor to conduct current through emittercollector to head lamps, and onto a second contact permitting current through emitter-base of transistor to fiow to tail lamps through armature and second contact.

. Summary of the invention This invention relates to light "sensitive control means and more particularly to light sensitive control means for automotive lighting systems which incorporate a time delay section to maintain the lighting system energized for a predetermined adjustable time period after the ignition circuit of the vehicle upon which it is mounted has been'switched oif and is an improvement over the light sensitive control system shown in US. Patent No. 3,274,- 434, issued Sept. 20, 1966 in the name of Charles W. Miller assigned to a common assignee. 5 Light sensitive control systems have been devised for automotive vehicles to switch on the lights when the ambient light level decreases below a predetermined value and to turn on said lights if'the ambient light level increases above that level. In the above identified Miller patent, time delay means is incorporated in a basic circuit to maintain the lights of the vehicle energized for a short adjustable period of time after the ignition system is switched off to permit the operator to proceed to another area before the lights are deenergized.

The present improvement in-such a system is to provide simpler means to control the primary lighting circuits of the vehicle from such a light sensitive control system.

It is a further object in making this invention to eliminate a power relay in a light-sensitive control system and substitute therefor a transistor to control the lamp circuits directly.

With these and other objects in view which will become apparent as the specification proceeds, my invention will be best understood by reference to the following specification and claims and the illustrations in the accompanying drawing, in which: i The figure is a circuit diagram of a light sensitive control system for vehicle lighting circuits embodying my invention.

Referring now more particularly to the drawing there is shown therein a primary control system including a light sensitive cell 2 and two transistors T-1 and T-2 which togetherwith their associated circuitry form the basic circuit. This circuit turns the vehicle lights on when the ambient light level decreases below a certain point and turns them ofi when the light level increases above a given figure. Themain control is provided by transistor T1 in combination with a sensitive relay 3' formed by coil 4 and its armature 6. The time delay feature previously mentioned for maintaining the lights in energized condition to permit the operator to reach a remote area after leaving his car is provided by the transistor T-Z and its associated circuitry. In the previous circuits in order to obtain proper switching of the actual lighting systems, the sensitive relay 3, controlled at power relay to actually switch the light circuits on and oif. In the present instance this power relay is eliminated and in its place there is substituted a transistor T-3 which controls the flow of current to the head-lamp and tail lamp circuits of the vehicle causing them to be energized or de-energized.

The main control transistor T-1 has its emitter 8 connected to a secondary power supply line 10 which in turn is connected through resistor 12 to terminal 14 of the light sensitive cell 2. It is also connected through diode 16 to a main power line 18 which is directly connected to the ignition energizing circuit as indicated by the label. A condenser 20 is connected across between emitter 8 and base 22 of the transistor T-l. Terminal 24 of the light cell 2 is connected to an adjustable tap 26 which is movable over the surface of resistance 28, one terminal of which is connected to the base 22 of transistor T-l and the opposite terminal connected to ground line 30. A limiting resistor 32 is connected between the juncture of diode 16 and resistance 12, to line 34 which extends between the collector 36 of transistor T-3 and the headlamps. Relay operating coil 4 is connected between collector 38 of transistor T-l and ground line 30 in such a manner that when the transistor T-l conducts and causes sufficient current to How through said coil 4 it will attract its armature 6 causing the same to pull down and move away from upper stationary contact 40 against which it is spring biased and down against lower contact 42. This lower contact is directly connected through line 44 with the tail lamps of the vehicle.

Relay armature 6 is connected byconductor 46 with the base 48 of transistor T-3. Secondary power line 10 is connected directly to emitter 50 of transistor T-2 and supplies the biasing voltage therefor. Collector 52 of transistor T-2 is connected through conductor 54 with base 22 of transistor T-1. Resistance 56 is connected between secondary power line 10 and ground line 30 and a second resistance 58 is connected between secondary power line 10 and the headlamp circuit. A movable switch arm 60 is directly connected to ground line 30 which switch arm when closed on its stationary contact 62 grounds the circuit. This switch is utilized to switch from manual to automatic operation. When the switch is closed the circuit is in position for automatic operation as the light sensitive control is energized. When it is open it is necessary for the operator to manually control the lights. The main power line 18 is connected to the base 64 of the transistor T-2 through two parallel circuits, one through a rectifier 66 and a resistance 68 in series and secondly through a resistance 70 having a variable tap 72 movable over its surface. This adjusts the time delay period. A condenser 74 is connected between base 64 of transistor T-2 and ground line 30. The vehicle battery is directly connected through line 76 to tie line 78 which extends between upper stationary contact 40 of the sensitive relay and emitter electrode 80 of the transistor T-3.

The operation of the circuit will now be described. Assuming that the driver has closed switch 60-62 to incorporate automatic control and also that the ignition switch is closed and the car is running, the light sensitive system is now energized. The position of the armature 6 of the sensitive relay is in the position assumed during daylight conditions or those of maximum ambient light on the light cell 2 and there is no necessity for the lighting system of the car to be energized. At this time voltage is applied to line 18 through the ignition switch and through diodes 16 and 66 to the secondary power line 10 and to the time delay system, respectively. At this time voltage on the light cell v2 and on the line 18 is substantially the same and the resistor 12 furnishes voltage to the emitters 8 and 50 of the transistors T-1 and T-Z. The bias on the base 22 of transistor T-l is high causing the sensitive relay 3 to be de-energized, allowing its armature 6 to be held up in the position shown and the vehicle lighting system will be deenergized for the following reasons. The emitter '80 of the transistor T-3 is directly fed by the car battery. The collector 36 is directly connected to the headlamps through line 34 and the base 48 is connected to the tail lamps through line 44 only when the armature 6 is in its lower or energized position. When the sensitive relay is in the position shown, no base current flows since the base and emitter are at the same potential and the transistor T-3 is cut oif hence no collector current flows and both headlamps and tail lamps are oil.

When the ambient light level on the light cell 2 decreases to a point where it is necessary to switch on the lights, the resistance of this light cell increases and current through the potentiometer 28-26 is reduced to a point changing the base bias on transistor T-l so that there is sufiicient current flowing through that transistor and of necessity through the relay coil 4 in series therewith to cause it to pull on its armature 6 to its engaging position away from stationary contact 40- and into engagement with contact 42. This breaks the voltage supply circuit to the base 48 and that is open circuited causing the base bias to change on transistor T-3 and the transistor can turn on so that current can flow therethrough to the headlamps energizing the same. The forward bias from emitter to base is also sufiicient to permit flow therethrough to feed the line 44 to energize the tail lamps. The ratio from turn off to turn on is obtained through resistor 58 from secondary power line 10 to the headlamps for the following reason. When the headlamps are off the lower terminal of this resistor is grounded through the headlamp filament. It is then in parallel with the resistor 56 from the emitter S to ground. The emitter of T-1 is thus maintained at a given voltage which when used in a normal automotive circuit may be 9 volts. When the headlamps are on, the resistor 58 is essentially in parallel with resistor 12 which is of considerably lower value and this raises the voltage at emitter 8 to a higher value as, in the example shown, perhaps 10 volts, thus requiring a higher light level to turn transistor T-1 off than that required to turn it on. T-3 operates to provide a separation between the circuits supplying the filaments of the tail lamps and headlamps and also eliminates the necessity for a large power relay for switching.

The delay portion of the circuit incorporating transistor T-2 forms no part of the present invention but does provide a delay in the de-energization of the lighting system 'when the operator parks the car and desires to leave :it in a darkened area. Assuming that the car has been operating and that the ambient light is at a very low level requiring illumination, the operator reaches an area Where he desires to leave the vehicle. He first shuts oil :the ignition system and this immediately removes the :supply voltage from power line 18. The car lighting system, however, remains energized. The lights now receive power through line 76 as before described, emitter 80, body of transistor T-3, collector 36 and through line 34 to headlamps, base 48, line 46, armature 6, line 44 to the tail lamps and through resistance 32 to the secondary power line 10 to maintain the transistors T-1 and T-2 energized. During the normal operation of the electrical system of the car the condenser 74 became charged to a predetermined degree and maintains this charge until the ignition switch is turned off and power line 18 becomes de-energized. Now the charge on capacitor 80 may leak off through adjustable rhesostat 70-72 to ground line 18. This causes the voltage on the base 64 of transistor T-2 to approach ground and transittor T-2 which has been biased off may now conduct. Current flow through transistor T-2 also flows through sensitivity control potentiometer 26-28 which raises the base potential of base 22 to cause transistor T-1 to cut olf releasing relay armature 6 of the sensitive relay 3 and, therefore, cutting off the lights after a predetermined delay period depending upon the setting of the potentiometer 70-72 which determines the time period of discharge of the condenser 74 and thus the length of time required to bring transistor T-2 to a conducting stage to cause such switching. Transistor T-2 is, therefore, non-conducting during all periods of operation of the lighting system of the car except for a few seconds when it is called into play after the ignition switch is turned off.

What is claimed is:

1. In a light sensitive control system, a plurality of load circuits that it is desired to control, a light sensitive device, a first transistor having an emitter, base and collector electrodes, a source of electrical power connected to said emitter to properly bias the first transistor, said light sensitive device being connected across the baseemitter electrodes, relay means including a coil and switching means actuated thereby, said coil being connected in circuit with said collector electrode and its energization controlled by conductivity of the first transistor, a second transistor having a base, emitter and collector electrodes, said emitter electrode of the second transistor being connected to the switching means and the source of electrical power, the collector electrode to one of the load circuits and the base to the switching means, said switching means also being connected to another of the load circuits so that as the light intensity on the light sensitive device changes it will vary conductance through the first transistor which controls the relay means and that in turn switches the load circuits through the second transistor.

2. In a light sensitive control system, a plurality of load circuits that it is desired to control, a light sensitive device, a first transistor having an emitter, base and collector electrodes, a source of electrical power connected to said emitter to properly bias the first transistor, said light sensitive device being connected across the base-emitter electrodes, relay means including a coil and switching means actuated thereby, said coil being connected in circuit with said collector electrode and its energization controlled by conductivity of the first transistor, a second transistor having a base, emitter and collector electrodes, said emitter electrode of the second transistor being connected to the switching means and the source of electrical power, the collector electrode to one of the load circuits and the base to the switching means, said switching means also being connected to another of the load circuits so that as the light intensity on the light sensitive device changes it will vary conductance through the first transistor which controls the relay means and that in turn switches the load circuits through the second transistor, and time delay means connected to the first transistor to maintain the same energized for a predetermined period after the first-named connection of the first transistor to the source of electrical power is broken.

3. In a light sensitive control system, a plurality of load circuits that it is desired to control, a light sensitive device, a first transistor having an emitter, base and collector electrodes, a source of electrical power connected to said emitter to properly bias the first transistor, said light sensitive device being connected 7 across the base-emitter electrodes, relay means including a coil and switching means actuated thereby, said coil being connected in circuit with said collector electrode and its energization controlled by conductivity of the first transistor, a second transistor having a base, emitter and collector electrodes, said emitter electrode of the second transistor being connected to the switching means and the source of electrical power, the collector electrode to one of the load circuits and the base to the switching means, said switching means also being connected to another of the load circuits so that as the light intensity on the light sensitive device changes it will vary conductancethrough the first transistor which controls the relay means and that in turn switches the load circuits through the second transistor, and resistance means connected between the emitter electrode of the first transistor and one of the load circuits to change the bias on the first transistor between periods of load energization and de-energization so that it requires differing amounts of light to switch the load circuits on than to hold them energized.

4. Apparatus for energizing the head lamps and tail lamps of an automotive vehicle in response to ambient light conditions comprising: a source of electrical power and a relay coil, a normally nonconductive switching device connected in series with the source and coil, -a light sensing device connected to render the switching device conductive when the ambient light decreases to a predetermined value, a transistor having emitter, collector and base electrodes, a switch having an armature controlled by the relay coil and first and second terminals which may be separately contacted by the armature, bias means connected to the first terminal, the tail lamps being connected to the second terminal, the armature being connected to the base electrode of the transistor, the source being connected to the emitter electrode and the head lamps being connected to the collector electrode, and means normally urging the armature into contact with the first terminal thereby to render the transistor nonconductive, but the last mentioned means being overridden by the relay coil, when energized, to bring the armature into contact with the second terminal thereby to render the transistor conductive, to energize the head lamps through the emitter-collector circuit of the transistor and to energize the tail lamps through the emitter-base circuit of the transistor, the armature and the second terminal.

References Cited UNITED STATES PATENTS 3,274,434 9/1966 Miller 315-82 3,280,374 10/1966 McCartney et al. 307-885 WALTER STOLWEI-N, Primary Examiner. 

4. APPARATUS FOR ENERGIZING THE HEAD LAMPS AND TAIL LAMPS OF AN AUTOMOTIVE VEHICLE IN RESPONSE TO AMBIENT LIGHT CONDITIONS COMPRISING: A SOURCE OF ELECTRICAL POWER AND A RELAY COIL, A NORMALLY NONCONDUCTIVE SWITCHING DEVICE CONNECTED IN SERIES WITH THE SOURCE AND COIL, A LIGHT SENSING DEVICE CONNECTED TO RENDER THE SWITCHING DEVICE CONDUCTIVE WHEN THE AMBIENT LIGH DECREASES TO A PREDETERMINED VALUE, A TRANSISTOR HAVING EMITTER, COLLECTOR AND BASE ELECTRODES, A SWITCH HAVING AN ARMATURE CONTROLLED BY THE RELAY COIL AND FIRST AND SECOND TERMINALS WHICH MAY BE SEPARATELY CONTACTED BY THE ARMATURE, BIAS MEANS CONNECTED TO THE FIRST TERMINAL, THE TAIL LAMPS BEING CONNECTED TO THE SECOND TERMINAL, THE ARMATURE BEING CONNECTED TO THE BASE ELECTRODE OF THE TRANSISTOR, THE SOURCE BEING CONNECTED TO THE EMITTER ELECTRODE AND THE HEAD 